Humans and other animals are able to perceive and process environmental conditions using various sensory attributes. For example, animal skin and hair provide tactile and flow sensing for perception in land and/or water environments. Synthetic (engineered) sensors, on the other hand, typically are constructed on many different physical principles, such as heat and resistance, in an attempt to obtain similar information. Animal sensory systems have attributes that are more elegant and efficient than known engineered sensors.
Engineered sensors, such as micromachined sensors, have been previously developed based on a number of sensing methods. Microfabrication offers benefits including high spatial resolution, fast time response, integrated signal processing, and potentially low costs. Examples of microfabricated sensors include thermal (hot-wire) anemometers and artificial haircells.
In numerous species, including humans, the biological haircell sensor serves as the building block for sensing systems with amazing capabilities. A typical haircell in animals provides a biological mechanoreceptor. FIG. 1 shows a demonstration of a spider receptor haircell sensor 10. The haircell 10 includes a cilium 12 attached to tissue 14 via a cuticular membrane 16. The cilium 12 is connected to a neuron 18. Bending the cilium 12, as shown in the right side of FIG. 1, affects a signal path, producing a changed signal. This change is used for reception.
The functions of animal haircells have been very closely studied by biologists over the years. However, in recent years, with the development of micromachining techniques, researchers have started to mimic the stimulus-transmission mechanism of biological sensing systems.
Artificial haircells have been produced by the present inventors and by others. One example artificial haircell provided by one or more of the present inventors is described in J. Chen, Z. Fan, J. Engel, and C. Liu, “Towards Modular Integrated Sensors: The Development of Artificial Haircell Sensors Using Efficient Fabrication Methods”, Proceedings of the 2003 IEEE/RSJ Intl. Conference on Intelligent Robots and Systems, Las Vegas, Nev., October 2003. This haircell is typically formed from bulk micromachining. It includes a silicon-based, in-plane fixed-free cantilever on a silicon substrate. A vertical silicon cilium is provided at a distal free end. A force or a flow, such as an external flow parallel to the substrate, impacts upon the vertical cilium. Due to a rigid connection between the in-plane cantilever and the vertical cilium, a mechanical bending element is transferred to the cantilever beam, inducing strain at the base of the cantilever beam. This strain is detected using a strain sensor.
In another example artificial haircell provided by one or more of the present inventors and also described in J. Chen et al., a cilium is anchored by one or more rigid metal supports. The cilium preferably is made of a surface micromachined polymer and includes a stiff permalloy plating. A strain gauge is attached at the base of the cilium and includes a resistor, such as a nichrome resistor, on a polyimide backing. When an external force is applied to the cilium, the cilium deflects, causing the strain gauge to stretch or compress. The resulting change in resistance is detected.
Yet another artificial haircell provided by the one or more of the present inventors, as disclosed in J. Engel, J. Chen, D. Bullen, and C. Liu, “Polyurethane Rubber as a MEMS Material: Characterization and Demonstration of an All-Polymer Two-Axis Artificial Haircell Flow Sensor,” 18th IEEE International Conference on Micro Electro Mechanical Systems, MEMS 2005, Miami Beach, Fla. USA, January 2005, includes a sensor made entirely of polymer materials from a substrate level up. Polyurethane elastomers are utilized for sensing and structures. Such a haircell can detect two-axis deflection of a vertical polyurethane cilium using, for example, a plurality of carbon-impregnated polyurethane force sensitive resistors disposed at a base of the cilium.